This application is based upon, claims the benefit of priority of, and incorporates by reference, the contents of Japanese Patent Applications No. 2002-110296 filed Apr. 12, 2002.
1. Field of the Invention
The present invention relates to a starter motor for starting internal combustion engines, and particularly to an improved magnet switch for use in such a starter motor.
2. Description of the Related Art
There is a need for a variety of improvements in starter motors to reduce harmful impacts on the environment. For example, engine starter motors should be lighter and more compact, and have greater durability to maintain or withstand frequent engine idling stops (what is called xe2x80x9ceco-runxe2x80x9d). Japanese Patent Laid-Open Publication No. Hei 9-68142 discloses a technique that reduces damage on the involved gears by ensuring enhanced gear engagement and lowering the current in the switch in order to reduce the size of the switch itself. More specifically, the current in the attraction switch has been reduced by more than 70%, the attraction coil has been downsized significantly, the ON and OFF switching of the main current and engagement with the ring gear of the pinion are performed with a plunger situated through the center of the coil, a rod moves together with the plunger shaft, and a movable contact and a hook are used for starting the engine. Some of the switches move the movable contact and the hook independently of the two separate rods, but because they move somewhat simultaneously while driven by an attraction force, the operation mechanism is common.
Although the improved engagement made the switch smaller, the electronic current that intermittently runs in the contact thereof does not change because it is determined by the necessary motor power. Consequently, since the current of the same magnitude runs the switch contact, the current density increases, and the contact is likely to wear at an anomalous rate. Moreover, since a thin rod must hold the contact and the hook (joint) at each end, the weight ratio of the contact and the hook grows, and the rod operation is affected by an increased load from the relatively heavy contact and hook. In addition, the sliding gap between the plunger and the inner circumference of the coil leads to instability in operation and results in such problems.
Meanwhile, although the thin rod (its diameter is approximately 2 mm) has to hold a small contact via an insulator washer for electric isolation, the insulator washer of poor mechanical strength often breaks during operation. In general, a contact current of about 700 A runs in the contact. Thus such a break-up of the insulator causes an absence of a safety gap, because the thickness of the insulator is 1 mm or less. Further, when the shock of the pinion engagement reaches the plunger and the contact via the hook, the thin, small rod contact and insulator are likely to break. To solve such problems, the contact may be maintained as large as before. However, this makes the thin rod have a large contact, and its operation becomes unstable. Specifically, the contact chatter by ON and OFF switching produces electric arks and may fuse the contact. Furthermore, as long as the rod exists inside the plunger, the saving of copper used in the coil is limited.
Since the plunger has key components (contact and hook) at both ends, both ends of the rod must be disposed outside the switch through the attraction coil thereof. Then the rod must be made of a non-magnetic material to utilize the magnet force of the coil. This non-magnetic material is usually an expensive material such as stainless steel or copper, which results in an expensive switch. Because the plunger must be assembled from the magnetic and non-magnetic parts in the small space in the attraction coil, the production cost becomes higher. If the rod is made of a magnetic material, all the magnetic flux runs in the rod, and the air gap does not have a magnetic flux. Then, no force to decrease the air gap is produced and the switch does not work.
To solve the above problems, an object of the present invention is to provide an inexpensive, reliable, compact switch which does not require special materials. The switch will not have a rod running through the plunger and fixed iron core while the contact and the hook are moved, not inside, but outside the attraction coil to reduce the size of the coil and maintain a sufficiently large contact.
In the magnet switch according to a first aspect of the present invention, the attraction coil has a plunger alone in its center, and this plunger is allowed to slide toward the side opposite to a fixed iron core. Thus it becomes possible to eliminate the non-magnetic rod from penetrating the fixed iron core, and the entire structure that forms a magnetic circuit can be made of iron. As a result, the inner circumference of the coil can be made small, and the plunger can also be made thin at no additional cost. Because the contact and the hook are formed on a thick plunger, instead of a thin rod, and the sliding gap between the rod and the plunger or fixed iron core becomes unnecessary, the operation of the contact is stable.
In the magnet switch according to a second aspect of the invention, the contact for current ON and OFF control is formed at one end of the switch, while the joint that drives the pinion is formed at the other end thereof, and they are connected to each other by a flange formed on the outer periphery of the case. Unlike the conventional thin rod, this flange interferes with nothing, so it can be made thick to be sufficiently strong. Then the flange can be large enough in terms of electrical and mechanical requirements with no need to enlarge the switch including an attraction coil and other parts.
In the magnet switch according to a third aspect of the invention, the contact holder is fixed via the flange arm extending from the outer periphery of the case. Thus even a large contact can be fixed with the holder from the outer periphery with a sufficient margin. If the holder is made of an electric insulator, the mechanical strength can be held high and the contact can securely work.
In the magnet switch according to a fourth aspect of the invention, the switch itself is firmly fixed in the starter, and the sliding unit such as the joint and the flange are covered with a cover that covers the contact room. Thus there is no need to add a separate dust cover or enlarge the outer diameter of the switch. Specifically, if the switch of the invention is installed in a usual starter, a separate large cover becomes necessary and its outer diameter becomes as large as the conventional switch. However, the structure of the invention is free from such drawbacks and is compact and durable against dust and water.
The magnet switch according to a fifth aspect of the invention is highly reliable and can be reduced in size. Engagement control makes the attraction coil current significantly small and permits a reduction in the size of the switch, while reducing production costs.
In the magnet switch according to a sixth aspect of the invention, the center of the attraction coil is made of a fixed iron core alone, and any non-magnetic rod penetrating the fixed iron core is not necessary. Additionally, all the parts can be made of iron to form a magnetic circuit. Thus, the inner circumference of the coil can be made thin, and as a result, the attraction coil can be made small and there is no substantial increase in costs. Because the contact and the hook are formed on a thick plunger, instead of a thin rod, and no sliding gap exists between the rod and the plunger or the fixed iron core, the operation of the contact is not affected. Moreover, since the magnetic circuit of the sliding unit of the plunger and case sidewalls is not the inner circumference of the case sidewalls as in a conventional case, but rather the outer circumference, the operation area becomes large, and accordingly the magnetic resistance becomes smaller. Because of this, the coil can be made smaller.
In the magnet switch according to a seventh aspect of the invention, the contact for current ON and OFF control is formed at one end of the switch, while the joint that drives the pinion is formed at the other end thereof, and they are connected to each other by a flange formed on the outer periphery of the case. Unlike the conventional thin rod, this flange interferes with nothing, therefore it can be made thick to be sufficiently strong. Then the flange can be large enough in terms of electrical and mechanical requirements with no need to enlarge the switch including an attraction coil and other parts.
In the magnet switch according to an eighth aspect of the invention, the contact holder is fixed via the flange arm extending from the outer periphery of the case. Thus even a large contact can be fixed with the holder from the outer periphery with a sufficient margin. If the holder is made of an electric insulator, the mechanical strength can be held high and the contact can securely work.
In the magnet switch according to a ninth aspect of the invention, the switch itself is firmly fixed in the starter, and the sliding unit, that is, the joint and the flange, are covered with a cover covering the contact room. Thus there is no need to add a separate dust cover or enlarge the outer diameter of the switch. Specifically, if the switch of the invention is installed in a usual starter, a separate large cover becomes necessary and its outer diameter becomes as large as the conventional switch. However, the structure of the invention is free from such drawbacks, is compact and durable against dust and water.
The magnet switch according to a tenth aspect of the invention is highly reliable, small in size, and can be made at a reduced cost. Engagement control makes the attraction coil current significantly small, which permits a reduction of the switch size.